1. Field of the Invention
The present invention relates generally to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device, which can improve the filling characteristic of a contact hole during the formation of metal wiring contact plug and can improve the operation characteristics of the device by reducing the parasitic capacitance of an inter-metal dielectric.
2. Description of the Prior Art
For higher integration of semiconductor devices, width of the metal wirings and breadth of the contact holes providing a path for electrical connection between the lower and upper metal wirings tend to decrease. However, the process of patterning a narrow-width wiring metal film as well as the process of fully filling a narrow or fine-sized contact hole become more and more difficult.
Further, the spacing between the metal wirings is shortened due to the high integration of the device, and this introduces more and more of parasitic capacitance caused by an Inter-Metal Dielectric (hereinafter referred to as “IMD”). Such parasitic capacitance is a main factor impeding the high-speed operation of the device.
Therefore, research has been directed to solving the above-mentioned problems related to the high integration of semiconductor devices and, as a part of such research, a proposal has been made to utilize amorphous carbon as a hard mask film for forming a metal wiring or to use the amorphous carbon as an IMD.
Amorphous carbon is easily removable like a photoresist film, but it can still be used as a hard mask because of its higher hardness than the photoresist film. The amorphous carbon also has a high etching selectivity ratio when compared to the other conventional hard mask materials. Thus, when the amorphous carbon is used as a hard mask material for metal film etching, a photoresist film pattern can be formed more thinly, and thus it is possible to prevent the collapse phenomenon or the Critical Dimension (CD) trimming from being caused by the increase in thickness of the photoresist film pattern, so as to obtain a metal wiring having a fine pattern.
Also, since amorphous carbon is a low-k material capable of reducing the parasitic capacitance, it can suppress a RC delay phenomenon, which can then elevate the operating speed of the semiconductor device when the amorphous carbon is applied as an IMD.
Hereinafter, a detailed description will be given of a semiconductor device manufacturing method including a process of forming a conventional metal wiring, in which amorphous carbon is applied as a hard mask and an IMD, with reference to FIGS. 1A to 1D.
Referring to FIG. 1A, a wiring metal film 110 is formed on a semiconductor substrate 100, and an amorphous carbon film 120 is formed on the wiring metal film 110. Next, an oxide film 130 is formed on the amorphous carbon film 120, and then a photoresist film 140 (which is for defining a wiring forming area) is formed on the oxide film 130. Here, the oxide film 130 functions as an antireflection film when the photoresist film 140 is etched, and is used as a hard mask for etching the amorphous carbon film 120.
Referring to FIG. 1B, the photoresist film 140 of FIG. 1A is etched through a lithography process including well-known exposure and etching processes to form a photoresist film pattern 140a defining the wiring forming area. Subsequently, a portion of the oxide film 130 under the photoresist film pattern 140a is etched by using the photoresist film pattern 140a as an etching barrier. During this process, the photoresist film pattern 140a suffers a partial loss in thickness. In succession, an exposed portion of the amorphous carbon film 120 is etched by using the residual photoresist film pattern 140a and the etched oxide film 130 as an etching barrier. During this process, the residual photoresist film pattern 140a may be lost completely.
Referring to FIG. 1C, in a state where the residual photoresist film pattern 140a and the etched oxide film 130 have been removed, the metal film 110 is etched by using the etched amorphous carbon film 120 as an etching barrier to form a metal wiring 110a. 
As stated above, when the amorphous carbon film 120 is used as a hard mask film for etching a wiring metal film 110, it is possible to prevent the collapse phenomenon which may occur when the photoresist film pattern is used or the CD trimming. This then makes possible to realize a metal wiring having a fine pattern even when a convention ArF exposure system is used—that is, it would also be possible to realize a metal wiring having a fine pattern even when an exposure system having a higher resolution than that of the ArF exposure system is not used.
Referring to FIG. 1D, in a state where the etched amorphous carbon film 120 has been removed, a low-k IMD 150 such as an amorphous carbon film is formed on the resultant structure such that the low-k IMD 150 covers the metal wiring 110a. 
Thereafter, although not shown in the drawings, the IMD 150 is etched to form a contact hole through which the metal wiring 110a is exposed. The contact hole is then filled with an electrically conductive contact plug film, and then well-known subsequent processes are successively performed to finally manufacture a semiconductor device.
However, in the prior art as described above, in which the low-k amorphous carbon film 150 is used as the IMD, the etching uniformity is not good during the etching process for forming the contact hole, and as a result a bowing phenomenon, in which the upper portion of the formed contact hole has a pot-like shape, occurs. This causes a problem in that a filling characteristic deteriorates when the contact hole is subsequently filled with the electrically conductive film, and it is difficult to ensure the reliability of a metal wiring including the contact plug. Because of this problem occurring when the contact hole is filled with the electrically conductive film, there is still a difficulty in applying the low-k material such as the amorphous carbon film capable of lowering parasitic capacitance to the IMD.